Railway traffic controlling apparatus



Nov. 19, 1935. R R KEMMERER ET AL 2,021,654

RAILWAY TRAFFIC CONTROLLING APPARATUS Eiled Jurie 22, 1954 2Sheets-Sheet 1 I s n g Q 2 w km 008 g v A mmM R C T F l a M@ A, wmlI LJIITI I mm U U BM 7 W M w B m ow ww ma a N aw K RN m QQQQQ THEIR ATTORNEYNOV. 19, 1935. R R, KEMMERER ET AL 2,021,654

RAILWAY TRAFFIC CONTROLLING APPARATUS 2 Sheets-Sheet 2 Filed June 22.1954 INVENTORS HaZp/z Rlaommemp T 11% ATTORN Patented Nov. 19, 1935UNITED TATES ATENT OFFICE RAILWAY TRAFFIC CONTROLLING APPARATUSApplication June 22, 1934, Serial No. 731,900

16 Claims. (01. 246-45) Our invention relates to railway trafiiccontrolling apparatus, and more specifically to apparatus for providingcontrol of signals in a wayside and/ or cab signaling system without theuse of control line Wires. Our invention also relates to the provisionof track circuit detection for the control of highway crossing signalsor other apparatus in a system of the above character.

We will describe several forms of railway trafiic controlling apparatusembodying our invention,

and will then point out the novel features thereof in claims.

Referring to the drawings, Fig. 1 is a diagrammatic view showing somecodes which may be used to control the apparatus embodying ourinvention. Fig. 2 is a diagrammatic view showing one form of apparatusembodying our invention, adapted for operation on direct current codes,and including a cut section which may be used for controlling highwaycrossing signals. Fig. 3 is a diagrammatic view showing a modificationof a portion of the apparatus of Fig. 2, also embodying our invention,in which alternating current codes for cab signal control may besuperimposed upon the direct current codes used for the control ofwayside signals. Fig. 4 is a diagrammatic view showing a furthermodification of the apparatus of Fig. 2, and also embodying ourinvention, in which alternating current codes are used throughout forsignal control. Fig. 5 is a diagrammatic view showing a modified form ofa portion of the apparatus illustrated in Fig. 2.

Similar reference characters refer to similar parts in each of theseveral views.

5 Referring to Fig. l, the three codes illustrated diagrammaticallytherein comprise periodically interrupted current which may be eitherdirect or alternating in character, according as it is desired to usetrack circuits and track relays of the direct current or alternatingcurrent type. Code A consists of periodically interrupted current ofnegative relative polarity; code B consists of periodically interruptedcurrent of positive relative polarity; and code C consists ofperiodically interrupted current in which positive and negative codeimpulses are alternated, that is, code C comprises periodicallypole-changed current. These codes are used for providing distinctivesignal indications in a manner which Will be clear from the descriptionof the remaining figures of the drawings.

Referring now to Fig. 2, we have shown a stretch of track divided intosections l2 and 2-3, in which traffic normally moves from left to right,in the direction of the arrow. At location 2, the track is intersectedby a highway, the intersection being protected by highway crossingsignals XS. As determined by trafiic conditions in advance, section i2maybe supplied with rail current of any one of the three codesillustrated in Fig. l. The rail current is supplied from a battery groupB B having its mid-point con nected to one rail of the track, by a Wireiii. The plus and minus terminals of the battery group are connected tocontact fingers ii and [4, respectively, of a constantly operating codetransmitter GT Code transmitter CT alternately closes contacts -42 andll-it, as well as contacts I l-i5 and I l-I6, and is shown supplyingrail current in accordance with code C to section 'l---2, over wire iiand the front points of contacts I8, l9, and 2B of the decoding relays JD and H respectively. Current of code A is supplied over wire 2 l, theback point of contact l9 and the front point of contact 2%, undercertain trafiic condi- 20 tions; whereas current of code B is suppliedover wire 22, the back point of contact 58, and the front points ofcontacts l9 and 20, under certain other traflic conditions.

Section 6-2 is provided with a pair of two-po- 25 sition track relays TRand TBA which are polarized in such a manner as to operate from adeenergized position to an energized position only if current of theproper polarity is applied thereto, and to return to the deenergizedposition when 30 current is removed therefrom. Any suitable polar relayhaving an armature biased to .a deenergized position in the absence ofcurrent may be used. The track relays TR and TRA are so arranged thatone reiay will follow only the positive code impulses, whereas the otherrelay will follow only the negative code impulses. The purpose served byrectifiers R and R is to block current of the undesired polarity fromone or the other track relay, thereby decreasing the load on the trackbattery B B Relays TR and TBA are sufficiently quick acting to followthe impulses of codes A, B, and C. Operated by the track relays TR andTRA isa group of decoding relays H, D, and J, which control theindications of a signal S govern the supply of code current to thesection in the rear of section I2; and also initiate the operation ofthe highway crossing apparatus at location 2.

When code A, which comprises negative current impulses, is supplied tosection l--2, relay TRA. will operate, alternately opening contact.22-23 and closing contact 22-24, whereupon relay J will pick up. Eachtime that contact 22-24 closes, relay J will receive an impulse ofcurrent to maintain this relay in the energized position. Pelay TR will,of course, be deenergized. Consequently, relay D will remaindeenergized, so that back contact 25-26 will be closed. Therefore, relayH will pick up and will be maintained energized due to the currentimpulses which it receives over the periodically closed contact 2223 ofrelay TRA, front contact 28 of relay J, and back contact 2526 of relayD. With relays J and H energized and relay D d-eenergized, signal S willprovide the Y/R indication, showing that the section immediately inadvance of location 3 is occupied, which means that one block in advanceof signal S is clear. Code B will, therefore, be supplied to the sectionimmediately in the rear of location I, over wire 29, the back point ofcontact I9 of relay D, and the front point of contact of relay H. Itwill be understood that relays J, D and H are sufficiently slow actingto bridge the operation of relays TRA and TR, on code.

When the train clears the block which begins at location 3, code Bcomprising positive current impulses will be supplied to section l-2, sothat relay TR will now become operated, and relay TRA will bedeenergized. The periodic closing of contact 3U-3i will cause relay D tobecome energized, whereupon front contact 2'i will close, and relay Hwill be maintained energized over the periodically closed contact 3B32of relay TR, and front contact 2521 of relay D. Relay J will, of course,be deenergized since relay TRA is not following code. Signal S will nowindicate Y/G showing that two blocks in advance of signal S are clear.The section in the rear of block l-3 will receive code C, over wire 33and the front points of contacts l9 and 20 of relays D and H,respectively.

When more than two blocks in advance of signal S are clear, section l-2will receive code 0 comprising periodically pole-changed current so thatboth relays TR and TRA will follow code, whereupon all three relays J,D, and H will be energized, and signals S will indicate G /R, or clear.From the above description, it will be understood that the relays J, D,and H reflect the condition of trafiic in advance of signal S inaccordance with the code received by section l2,

Since sections l-Z and 23 are cut sections of the block |3, it followsthat whenever block l3 is unoccupied, both sections |2 and 23 willreceive the same code. That is, when section 2-3 receives code C, forexample, this code will be repeated into section I2 through theselective operation of relays H D and J and similarly for codes A and B.Since the polarities of adjoining track circuits are staggered for thepurpose of improving the broken down rail joint protection, it isnecessary to reverse the track leads 4| and 42 of alternate track relaygroups in order that the TRA relays will always operate on current ofnegative relative polarity, and the TR relays on current of positiverelative polarity. This procedure makes possible a uni form arrangementof the H, D, and J decoding relays. Obviously, by interchanging relaysTR and TRA, codes A and B can be interchanged, since from the standpointof safety it is immaterial which of these two codes is used forestablishing the desired signal indication.

We shall now describe the manner in which track circuit detection isobtained and made use of in the control of the highway crossing signalsXS at location 2. Normally, with block |-3 clear of traffic, bothwindings 34 and 35 of the interlocking relay XR which controls theoperation of the crossing signals, are energized so that signals XSremain inoperative. When a train enters section |--2 from the left,relays H, D and J will all be deenergized, and the circuit for winding34 of relay XR, which circuit includes the control wire 44, will beinterrupted at contact 36 of relay D, as well as at contact 31 of relayH, so that back contact 38 of relay XR will close. The closing ofcontact 38 initiates the operation of the crossing signals XS, the usualflasher relay and lamp control circuits being not shown, since these areWell known and form no part of our invention.

When the train enters section 2--3, relays H D and J will all bedeenergized, and the circuit for winding 35 of relay XR will beinterrupted at front contact 39 of relay H However, since winding 34 wasthe first to release its associated contact 38, back contact 40 will beprevented from closing, by the usual latching arrangement with which theinterlocking relay is provided. Signals XS will continue to operateuntil the train completely vacates section l-2. It will be noted thatwhen relays H D and J are deenergized, section l-2 is supplied withsteady current of positive relative polarity over the back point ofcontact 29 of relay H This steady current will cause relay TR to pickup, closing contact 3B3I, whereupon relay D will become energized. Assoon as relay D picks up, winding 34 of relay XR will become energizedover contact 36 of relay D, so that signals XS will be restored to theinoperative condition due to the opening of back contact 38 of relay XR.It follows, therefore, that steady or uncoded energy may be used in themanner described for providing track circuit detection.

If a train should back into section 2-3, relays H D and J will becomedeenergized and crossing protection will be provided through the openingof front contact 39 of relay H which deenergizes winding 35 of relay XRand sets signals XS into operation.

If there are more than two out sections within a block, the polarity ofthe steady current which is used for clearing out purposes may bestaggered in cut sections which adjoin, so that the broken down railjoint protection will extend to the track clearing apparatus. Thestaggering of the steady current may be readily accomplished bydisconnecting wire 43 afrom the positive terminal of battery B andconnecting it to the negative terminal of battery B When steady negativecurrent is used for clearing purposes, front contact 35 of relay Dshould be replaced by a front contact of relay J, since relay TR and.consequently relay D will not respond when negative current is fed tothe section.

Referring to Fig. 3, the form of the invention disclosed in this figureis similar to Fig. 2, except that provision is made for superimposingalternating current codes for the control of locomotive cab signals,upon the direct current codes A, B, and D, which control the waysidesignals. The system of track relays TR and TRA is identical with thetrack relay system of Fig. '2 except that a reactor X is inserted in oneof the track leads for the purpose of limiting the amount of alternatingcurrent which is permitted to flow in the track relay windings.Similarly, the system of decoding relays H D and J and the method ofcontrolling the associated wayside signal S are the same as in Fig. 2,so

that it is unnecessary to repeat in detail how these portions of thesystem operate.

It will be noted that in addition to the battery B ---l3 which furnishesdirect track circuit current for operating the track relays TR and TRA,we have provided a track transformer T which has a primary windingconstantly energized from an alternating current source BXCX and whichsupplies alternating current for cab signal control from its secondarywinding. The secondary winding of transformer T is connected in serieswith one or the other half of the battery B B and includes one oranother of the code transmitter contacts 86, I20, or [80, as determinedby traffic conditions in advance which, in turn, are reflected in theenergized or deenergized condition of the relays H D and J Thecontinuously operating code transmitter GT serves, therefore, not onlyto interrupt periodically the battery current for establishing the threewayside signal control codes A, B, and D, but also provides the threecab signal control codes comprising alternating current which isperiodically interrupted at the rate of 80, 120, or 180 times perminute, by the contacts 80, I20, and I80, respectively. In this manner,it becomes possible to operate locomotives equipped with frequency codedecoding equipment of standard type over territory provided with waysidecircuits and apparatus of the type herein disclosed.

Contacts 80 and I of the code transmitter GT are designed to providesubstantially equal on and off code intervals. Due to the fact thatcontact I85 must pole-change the direct current to establish code D, andat the same time must establish the equal on and off intervals of the180 code, this contact must provide a transfer time interval between thefront and back contact points of substantially equal duration to one ofthe on intervals of the code. That is, the transfer time between frontand back points of contact i813 represents an off code interval.

The manner in which the supply of track current is controlled by thedecoding relays is the same as in Fig. 2. That is, if three blocks ormore, in advance of signal S are unoccupied, all three of the decodingrelays H D and J will-be energized, and contact I80 will feed code D, aswell as 180 code, to the rails of the rear section, over the frontpoints of contacts [9 and 20 of relays D and H respectively. If but twoblocks in advance of signal S are unoccupied, relays D and H will beenergized, and relay J will be deenergized. The codes supplied to therear section under this condition will remain as before; that is, code Dfor wayside control and 180 code for cab signaling.

If but one block in advance of signal S is clear, relays J and 1-1 willbe energized, and relay D will be deenergized. Under this condition, therear section will receive code B and 120 code, over contact I20, theback point of contact 49 of relay D and the front point of contact 20 ofrelay H If block 45 is occupied, relays J D and 1-1 will all bedeenergized, and the rear section will receive code A and 80 code, overcontact BI and the back point of contact 20 of relay H It will be notedtha in the case of Fig. 3, the impulses in codes A, B, and D are notuniform in the three codes, as they are in the codes illustrated in Fig.1 which are used in the arrangement shown in Fig. -2. The reason forthis is that code D is produced by a contact which operates at the rateof 180 times per minute, whereas codes B and A are produced by contactswhich operate at the rates of 120 and 80 times per minute, respectively.However, no disadvantage 5 results from this non-uniformity, providedthat relays TR and TBA are sufficiently rapid to follow the relativelyfast impulses of code D, and relays J, D, and H are sufliciently slowacting to bridge the slower impulses of code A.

Referring to Fig. 4, the circuits of this figure are substantially thesame as those shown in Fig. 2, with the exception that in Fig. 4, codesA, B, and D comprise alternating current impulses and are used forcontrolling alternating 15 current track circuits, whereby the same railcurrent may be used for controlling both wayside and cab signalingapparatus.

The three codes A, B, and D are now supplied from a transformer TAhaving a mid-tap on the secondary at terminal CXA, in addition to theend terminals BXA and NXA. Code A comprises periodically interruptedalternating current of negative relative instantaneous polarity and issupplied to track transformer T from terminals NXA-CXA of transformerTA, over the 80 code contact of code transmitter CT and the back pointof contact 2%! of relay H Code B comprises periodically interruptedalternating current of positive relative instantaneous polarity and issupplied from terminals BXACXA of transformer TA, over the 120 codecontact of transmitter CT and the back point of contact i9 of, relay Das well as the front point of contact 29 of relay H Similarly, code Dcomprises periodically reversed current supplied alternately fromterminals BXA-CXA and NXACXA of transformer TA, over the 180 codecontact of transmitter CT and the front points of contacts is and 29 ofrelays D and H respectively. The 0 operation of contact ISQ oftransmitter CT is similar to the operation of the corresponding contactI80 of transmitter CT of Fig. 3, in that the of? code interval isproduced during the transit time of contact 985) between its front and 4back points.

It will be apparent from the foregoing that the instantaneous relativepolarities of the impulses in codes A and B are opposite, so that byproperly connecting the control windings of the two-element two-positionalternating current track relays TR and TRA to the track, relay 'I'RAwill respond only to impulses of code A, whereas relay TR will respondonly to impulses of code B, both relays responding alternately to codeD. In this manner, the same selective code response of relays J D and Hmay be obtained as previously described in connection with Figs.

2 and 3. The manner in which the circuits of Fig. 4 provide signalcontrol in accordance with 60 traffic conditions in advance will,therefore, be clear without added description. Should section 6-4contain a highway crossing, or should it be desired to provide traindetection for any other purpose, a detection circuit such as that shown66 in Fig. 2 at wire 44 and contacts 36 and 3'! of relays D and H,respectively, can be readily incorporated into Fig. i. for this purpose.Accord- 'ingly, steady or uncoded alternating current of one or theother relative instantaneous polarity 70 (with respect to the mid-tapCXA of transformer TA) may be used as the detection current, in themanner previously described in connection With Fig. 2.

Referring to Fig. 5, the circuit shown in this "s figure is amodification of the detection circuit or highway crossing controlcircuit of Fig. 2. In the case of the Fig. 2 circuit, there is a remotepossibility of incorrect operation, should one or the other of the trackrelays TR, TRA, fail to release due to the occurrence of some mechanicaldefect, or other cause, at the instant that a train enters section I2.Under the above condition, relay D, or relay J will be maintainedenergized, and contact 36 will remain closed, thus preventing therelease of relay XR which initiates operation of the highway crossingprotection. To avoid this condition, we have provided an additionalrelay K which checks that the track relays TR and TRA are deenergizedupon the entrance of a train into the section, and which also requiresthat the proper track relay be energized and relay K picked up beforethe highway crossing apparatus can be restored to normal, upon the exitof a train.

Under normal conditions, with no train in the associated track section,relay K remains deenergized. When a train enters the section, trackrelays TR and TRA will both be deenergized, so that contacts 38-32 and22-43 will remain closed, and any of the relays J, D, and H which mayhave been energized will release. The release of relay H opens theenergizing circuit for wire 44 at the front point of contact 31 of relayH, so that operation of the highway crossing apparatus is initiated.Relay K will now pick up over a circuit which includes back contact3032, wires 53 and 54, back contact 55 of relay D, wire 46, back contact41 of relay H, and wire 48, to the winding of relay K. The pick-up ofrelay K closes contact 5|, but wire 44 does not become energized due tothe fact that front contact 52 of relay D remains open.

As long as the train remains in the section, relay K will remainenergized. Upon the exit of the train, relay TR will pick-up on steadyenergy, and relay D will be picked up over contact 36-3 I. As soon as font contact 52 of relay D closes, wire 44 will become energized, toclear out the highway crossing apparatus, because front contact 5i ofrelay K, and back contact 31 of relay H will both be closed at thistime. Relay K will remain energized over a stick circuit which includescontact SEE-3i, wire 49, front contact 50 of relay K, wire 46, backcontact 41 of relay H, and wire 48, to the winding of relay K. RelaysTR, D, and K will all remain picked up until the train completely clearssection 2-3, at which time the steady energy in block |2 will bereplaced by coded energy supplied in accordance with code A. Relay Kwill remain energized for a short interval following the application ofcode to relay TRA, until relays J and H pick up. Relay H will pick upafter a few operations of contact finger 22, over contact 22-23, wire45, front contact 28 of relay J, and back contact 2526 of relay D. Assoon as relay H picks up, the energizing circuit for wire 44 will betransferred to front contact 31 of relay H, and the stick circuit forrelay K will be interrupted at back contact 41, so that relay K willrelease and the apparatus will be restored to its normal condition.

It will be apparent from the foregoing description of Fig. 5 that shouldrelay TR fail to release due to some mechanical defect or other cause,upon the entry of a train, operation of the highway crossing apparatuswill be initiated, nevertheless, because the energizing circuit for wire44 will be open at front contact 5| of relay K. Furthermore, completeclearing out of the apparatus,

following the exit of a train will not occur, unless relay K is firstpicked up, and then released; the release of relay K being impossibleunless contact finger 22 operates periodically, thus checking that relayTRA is following the impulses 5 of the code.

Although we have herein shown and described only a few forms of railwaytraific controlling apparatus embodying our invention, it is understoodthat various changes and modifications may 10 be made therein within thescope of the appended claims without departing from the spirit and scopeof our invention.

Having thus described our invention, what we claim is: 15 1. Incombination, a section of railway track,

means for at times supplying the rails of said section with periodicallyvaried current of reverse relative polarity and at other times withperiodically varied current of normal relative 20 polarity, a firstpolar relay receiving energy from said rails and responsive to currentimpulses of reverse relative polarity only, a second polar relayreceiving energy from said rails and responsive to current impulses ofnormal relative polarity 25 only, a contact of said first relay includedin the energizing circuit for said second relay, a contact or" saidsecond relay included in the energizing circuit for said first relay,and signaling apparatus controlled by said first and second relays. 80

2. In combination, a section of railway track, means for at timessupplying the rails of said section with coded current of reversepolarity and at other times with coded current of normal polarity, a metand a second code following 86 polar relay selectively responsive tocode current impulses of reverse and normal polarity respectively, acircuit for energizing said first relay connected across the rails ofsaid section and including a first rectifier poled in such manner 40 asto permit current of reverse polarity to flow in said first relay, acircuit for energizing said second relay connected across the rails ofsaid section and including a second rectifier poled in such manner as topermit current of normal 45 polarity to flow in said second relay, andsignaling apparatus selectively controlled by said first and secondrelays according as one or the other of said relays is following saidcode current impulses. 50

3. In combination, a section of railway track, means for at timessupplying the rails of said section with periodically varied current ofreverse polarity and at other times with periodically varied current ofnormal polarity, a first 55 and a second polar relay selectivelyresponsive to periodic current impulses of reverse and normal polarityrespectively, a first circuit for energizing said first relay connectedacross the rails of said section and including a first rectifier poled60 to permit current of reverse polarityto flow in said first relay, asecond circuit for energizing said second relay connected across therails of said section and including a second rectifier poled to permitcurrent of normal polarity to flow in said second relay, a contact ofsaid first relay included in said second circuit, a contact of saidsecond relay included in said first circuit, and signaling apparatuscontrolled by said first and second relays.

4. In combination, a section of railway track, means for at timessupplying the rails of said section with periodically varied current ofreverse polarity and at other times with periodically varied current ofnormal polarity, a. first polar relay v receiving energy from said railsand responsive to current impulses of reverse polarity only, a secondpolar relay receiving energy from said rails and. responsive to currentimpulses of normal polarity only, three decoding relays controlled bysaid first and second polar relays in such manner that the first andthird decoding relays become energized when said first polar relay isoperating and said second andthird decoding relays become energizedwhensaid second polar relay is operating, and signaling apparatus controlledby said decoding relays.

5. In combination, a section of railway track, means for at timessupplying the rails of said section with periodically varied current ofreverse polarity and at other times with periodically varied current ofnormal polarity and at still other times with current of alternatelynormal and reverse polarity, a first polar relay receiving energy fromsaid rails and responsive to current impulses of reverse polarity only,a second polar relay receiving energy from said rails means for at timessupplying the rails of said section with periodically varied current ofreverse polarity and at other times with periodically varied current ofnormal polarity and at stillother times with current of alternatelynormal and reverse polarity, a first polar relay receiving energy fromsaid rails and responsive to current impulses of reverse polarity only,a second polar relay receiving energy from said rails and responsive tocurrent impulses of normal polarity only; a contact of said first polarrelay included in the energizing circuit for said second polar relay, acontact of said second polar relay included in the energizing circuitfor said first polar relay; three decoding relays controlled by saidfirst and second polar relays in such manner that the first and thirddecoding relays become energized when said first polar relay isoperating, said second and third decoding relays become energized whensaid second polar relay is operating, and all three decoding relaysbecome energized when both of said polar relays are operating; andsignaling apparatus controlled by said decoding relays.

'7. In combination, a section of railway track, means for at timessupplying the rails of said section with periodically varied current ofreverse polarity and at other times with periodically varied current ofnormal polarity and at still other times with current of alternatelynormal and reverse polarity, a first polar relay receiving energy fromsaid rails and responsive to current impulses of reverse polarity only,a second polar relay receiving current from said rails and responsive tocurrent impulses of normal polarity only, three decoding relays, meansincluding a front contact of said first polar relay for energizing thefirst of said decoding relays, means including a front contact of saidsecond polar relay for energizing the second of said decoding relays;means for at times energizing the third of 8. In combination, a sectionof railway track,

means for at times supplying the rails of said section with periodicallyvaried current of reverse polarity and at other times with periodicallyvaried current of normal polarity and at still other times. with steadycurrent, a first polar relay receiving energy from said rails andresponsive to current impulses of reverse polarity only, a second polarrelay receiving energy from said rails and responsive to currentimpulses of normal polarity only; and signaling apparatus selectivelycontrolled according as one of said relays is steadily energized or oneor the other of said relays is following normal or reverse currentimpulses respectively.

9. In combination, a section of railway track &

intersected by a highway; means for supplying one or another of threesignal controlling codes comprising periodically varied current ofreverse polarity, periodically varied current of normal polarity,current of alternately normal and re- 0 verse polarity, and forsupplying steady track clearing current to the rails of said section,said three codes and said steady current being selected in accordancewith trafiic conditions in advance of said section; a first polar relayreceiving energy from said rails and responsive to current impulses ofreverse polarity only, a second polar relay receiving energy from saidrails and responsive to current impulses of positive polarity only; awayside signal controlled by said two relays in such manner as toprovide one of four indications according as said first relay isoperating on code current of reverse polarity, said second relay isoperating on code current of normal polarity, both said relays areoperating on code current of alternately normal and reverse polarity, orneither of said relays is operating; and means controlled by one of saidtwo relays effective when said one relay is energized by said trackclearing current for controlling signaling apparatus at said highwayintersection. 10. In combination, a section of railway track intersectedby a highway, means for supplying periodically varied current of reverseor of normal polarity, respectively, to the rails of said sectionaccording as the next section in advance is occupied or unoccupied, afirst polar relay receiving energy from said rails and responsive tocurrent impulses of reverse polarity only, a second polar relayreceiving energy from said rails and responsive to current impulses ofnormal polarity only, signaling apparatus controlled by said two relays,highway crossing apparatus at said highway intersection controlled bysaid two relays in such manner as to become operated when a train enterssaid section and both of said relays are released, means effective whenthe train clears said highway intersection for supplying steady currentto the rails of said section whereby one of said two relays will becomesteadily energized, and means effective when said one relay is steadilyenergized for restoring said highway crossing apparatus to theinoperative condition.

11. In combination, a section of railway track intersected by a highway,means for at times supplying the rails of said section with periodicallyvaried current of reverse polarity and at other times with periodicallyvaried current of normal polarity and at still other times with steadycurrent, a first polar relay receiving energy from said rails andresponsive to current impulses of reverse polarity only, a second polarrelay receiving energy from said rails and responsive to currentimpulses of normal polarity only, three decoding relays, means includinga front contact of said first polar relay for energizing the firstdecoding relay, means including a front contact of said second polarrelay for energizing the sec-' ond decoding relay; means for at timesenergizing the third decoding relay over a circuit including a backcontact of said first polar relay and a front and a back contact of thefirst and second decoding relays respectively, and for at other timesenergizing said third decoding relay over a circuit including a backcontact of said second polar relay and a front contact of said seconddecoding relay; a wayside signal controlled by said three decodingrelays, highway crossing apparatus at said highway intersection, acontrol relay for governing said crossing apparatus, and an energizingcircuit for said control relay including a front contact of one of saiddecoding relays.

12. In combination, a section of railway track intersected by a highway,means for at times supplying the rails of said section with periodicallyvaried current of reverse polarity and at other times with periodicallyvaried current of normal polarity and at still other times with steadycurrent, a first polar relay receiving energy from said rails andresponsive to current impulses of reverse polarity only, a second polarrelay receiving energy from said rails and responsive to currentimpulses of normal polarity only, three decoding relays, means includinga front contact of said first polar relay for energizing the firstdecoding relay, means including a front contact of said second polarrelay for energizing the second recoding relay; means for at timesenergizing the third decoding relay over a circuit including a backcontact of said first polar relay and a front and a back contact of thefirst and second decoding relays respectively, and for at other timesenergizing said third decoding relay over a circuit including a backcontact of said second polar relay and a front contact of said seconddecoding relay; a wayside signal controlled by said three decodingrelays, highway crossing apparatus at said highway intersection, acontrol relay for governing said crossing apparatus, and two energizingcircuits for said control relay one of which includes a front contact ofsaid third decoding relay and the other of which includes a frontcontact of one of the remaining two decoding relays as determined by thepolarity of the steady current supplied to the rails of said section.

13. In combination, a section of railway track, means for at timessupplying the rails of said section with coded alternating current ofreverse instantaneous relative polarity and at other times with codedalternating current of normal instantaneous relative polarity, a firsttwo-element relay receiving energy from said rails and responsive torail current impulses of said reverse relative polarity only, a secondtwo-element relay receiving energy from said rails and responsive torail current impulses of said normal relative polarity only, a contactof said first relay included in the energizing circuit for one elementof said second relay, a contact of said second relay included in theenergizing circuit for one element of said first relay, and signalingapparatus controlled by said first and second relays.

14. In combination, a section of railway track,

means for at times supplying the rails of said section with a first codefor controlling wayside signals as well as cab signals, said first codecomprising alternating current of reverse instantaneous relativepolarity periodically varied at 10 a first frequency, means for at othertimes supplying the rails of said section with a second code forcontrolling wayside signals as well as cab signals, said second'codecomprising alternating current of normal instantaneous relative polarityperiodically varied at a second frequency, a first two-element relayreceiving energy from said rails and responsive to rail current impulsesof said reverse polarity only, a second twoelement relay receivingenergy from said rails and responsive to rail current impulses of saidnormal polarity only, a contact of said first relay included in theenergizing circuit for one element of said second relay, a contact ofsaid second relay included in the energizing circuit for said firstrelay, and signaling apparatus controlled by said first and secondrelays.

15. In combination, a section of railway track, means for at timessupplying the rails of said section with periodically variedunidirectional current of reverse polarity and at other times withperiodically varied unidirectional current of normal polarity and atstill other times with current of alternately normal and reversepolarity, a first polar relay receiving energy from said rails andresponsive to current impulses of reverse polarity only, a second polarrelay receiving energy from said rails and responsive to currentimpulses of normal polarity only, means effective when the first of saidtwo relays is operating for supplying the rails of the rear sectionwhich adjoins said given section with periodically varied unidirectionalcurrent of normal polarity for wayside signal control as well as withalternating current periodically varied at a first frequency for cabsignal control, means effective when the second of said two relays isoperating for supplying the rails of said rear section withunidirectional current of alternately normal and reverse polarity forwayside signal control as well as with alternating current periodicallyvaried at a second frequency for cab signal control, and a waysidesignal controlled by said two relays.

16. In combination, a section of railway track intersected by a highway,means for at times supplying the rails of said section with periodicallyvaried current of reverse polarity and at other times with periodicallyvaried current of normal polarity and at still other times with steadycurrent, a first polar relay receiving energy from said rails andresponsive to current impulses of reverse polarity only, a second polarrelay receiving energy from said rails and responsive to currentimpulses of normal polarity only, three decoding relays, means effectivewhen said first polar relay is operating for energizing the first andthird of said decoding relays, means effective when said second polarrelay is operating for energizing the second and third of said decodingrelays, a slow acting relay, a pickup circuit for said slow acting relayincluding a back contact of said first polar relay and a back contact ofboth said first and third decoding relays; a stick circuit for said slowacting relay including a front contact of said first polar relay,

a front contact of the slow acting relay, and said back contact of thethird decoding relay; a wayside signal controlled by said three decodingrelays, highway crossing apparatus at said highway intersection, acontrol relay for governing said crossing apparatus, and two energizingcircuits for said control relay one of which includes a front contact ofsaid third decoding relay, and the other of which includes a frontcontact of said slow acting relay, a front contact of said firstdecoding relay, and a back contact of said third decoding relay.

RALPH R. KEMMERER. ROBERT M. GILSON.

